Critical dimension (CD) control is a challenge during semiconductor substrate manufacturing steps such as plasma etching. The uniformity of CD across the substrate can also affect the yield of chips from the substrate. In known semiconductor manufacturing nodes, a CD uniformity of <1 nm can be specified.
Controlling temperature is not an easy task for several reasons. First, many factors can affect heat transfer, such as the locations of heat sources and heat sinks, and the movement, materials and shapes of the media. Second, heat transfer is a dynamic process. Unless the system in question is in heat equilibrium, heat transfer can occur and the temperature profile and heat transfer will change with time. Third, non-equilibrium phenomena, such as plasma, which of course is always present in plasma processing, make the theoretical prediction of heat transfer behavior of any practical plasma processing apparatus very difficult if not impossible.
The substrate temperature profile in a plasma processing apparatus is affected by many factors, such as the plasma density profile, the radio frequency (RF) power profile and the detailed structure of the various heating and cooling elements in the electrostatic chuck assembly, hence the substrate temperature profile is often not uniform and difficult to control with a small number of heating or cooling elements. This deficiency translates to non-uniformity in the processing rate across the whole substrate and non-uniformity in the critical dimension of the device dies on the substrate.